1. Field of the Invention
The present invention relates in general to disk storage systems and more particularly, to a method and apparatus for providing and storing skew offset information for aligning the read element of a magneto-resistive (MR) head with the centerline of written data during a read operation.
2. Description of the Related Art
Disk drives are magnetic recording devices used for the storage of information. The information is recorded on concentric tracks on either surface of one or more magnetic recording disks. The disks are rotatably mounted to a spin motor and information is accessed by means of read/write heads that are mounted to actuator arms which are rotated by a voice coil motor. The voice coil motor is excited with a current to rotate the actuator and move the heads. The read/write heads must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information.
To accurately write and read data, it is desirable to maintain the head on the center of the track. To assist in controlling the position of the head, each sector of the disk typically contains a number of servo bits accurately located relative to the centerline of the track. The signals produced by the servo bits are typically demodulated into position offset signals which are used to determine the position of the head relative to the track, and to move the actuator arm if the head is not located on the track centerline.
There has been developed a dual element transducer which includes a single write element and a separate read element which is constructed from a magneto-resistive material. Such dual element transducers are commonly referred to as magneto-resistive (MR) heads. Because of manufacturing tolerances, the separate magneto-resistive read element may be off-center or skewed from the write element of the head. Therefore, if data is written off the center of the track, to read the data, the servo system must move the head slightly off-center so that the read element is centered with the written data.
Additionally, while the head and write elements may be aligned with the head is positioned over a particular track, when the head is moved to another track, the read element may no longer be aligned with the write element. For example, as shown in FIGS. 1A and 1B, when the head is positioned over a track along the outer diameter of the disk, the centers of the read and write elements (R and W respectively) are aligned. However, as shown in FIGS. 2A and 2B, when the head is positioned over a track along the inner diameter of the disk, the centers of the read R and write W elements are no longer aligned. The servo system must move the head slightly off-center, so that the read element R is centered with the written data. The routine of moving an MR head during a read operation is commonly referred to as micro-jogging.
It also has been determined that the skew offset information for an MR head located over the inner tracks of a disk is different from that of an MR head located over the outer tracks of a disk. In addition, such MR head skew offset information is typically non-linear, and it also generally varies greatly between heads.
Accordingly, there is a need in the technology for a method and apparatus for providing skew offset information used in the alignment of a magneto resistive head, so that a read element of an MR head may be aligned with the centerline of written data during a read operation.
In non-MR servo systems, the stored parameters are read during a power up sequence so as to optimize the performance for the particular drive. In systems utilizing an MR head, the data written on the dedicated tracks may not be centered exactly on the tracks because the read and write heads are offset. As a result, when the system attempts to read the written data, additional time is required to locate the centerline of written data. Alternatively, several attempts to read the written data may be required before successfully acquiring the written data. To compound this problem, the associated parameters are typically written on the outermost tracks of the disk where the largest offset between the read and write elements generally occurs.
Accordingly, there is also a need in the technology for an apparatus and method of storing system parameters so that hard drive assemblies utilizing MR heads may efficiently retrieve the stored information.